1. Field of the Invention
The present invention relates to a novel graft copolymer comprising a silicone backbone and having polylactone grafts linked thereto via urethane bonds, a process for the preparation thereof, and to the use of such graft copolymer, especially for biomedical applications, as an additive for polymer compositions, in particular for compositions based on polyvinyl chloride and copolymers thereof.
2. Description of the Prior Art
It is known to this art to prepare polydiorganosiloxane and polyurethane block copolymers optionally comprising polyester linkages. See French Pat. No. 1,291,937.
French Pat. No. 1,427,660 describes the use of addition products of organopolysiloxanes and of polyisocyanates, which may be the same as those described in said French Pat. No. 1,291,937, as additives for polyvinyl chloride in a proportion of from 0.01 to 30% by weight of additive to improve such PVC processing parameters as extrusion, calandering, and the like.
In French Pat. No. 2,005,037 block copolymers are generally described, including polysiloxane-polylactone which may be employed as an additive to modify the surface properties of PVC, without explicitly referring to biomedical applications thereof, and features a particular polysiloxane-polylactone block copolymer.
In French Pat. No. 2,007,788, compositions are described which contain copolymers including blocks of lactone and polysiloxane which can be employed as surface-active agents and/or foam stabilizers in foam manufacture, the polysiloxane and polylactone blocks being linked via an organic connecting bridge containing from 2 to 12 carbon atoms, albeit no mention is made of a urethane such linkage.
And in French Pat. No. 2,017,527 are described copolymers comprising polysiloxane and polyetherurethane blocks, the said blocks being joined via silicon-nitrogen bonds, and such copolymers exhibiting high blood-compatibility.
Blood-compatible block polymers containing a series of polyalkylsiloxane, polyurethane or polyureaurethane and polyalkylene oxide blocks are described in French Pat. Nos. 2,491,938 and 2,497,217. The possibility of graft copolymers is referred to at page 8, lines 9 to 20, and page 11, lines 9 to 14, respecting a polydimethylsiloxane containing hydroxyalkyl end groups, but such graft copolymers are not explicitly described.
Moreover, the linking of a polylactone to a polysiloxane bearing hydroxyalkyl groups in the chain via a urethane bridge is neither suggested nor described.